NT Authority System shutdown & lsass.exe error

I have an XP Pro with SP3. I was using the computer with no problems when I noticed the automatic update shield in the task bar. I clicked on it and it vanished only to reappear a few minutes later. This process repeated several times without actually installing anything so I rebooted my computer just to see if it would stop. Ever since then I keep getting this error:

"This shutdown was initiated by NT Authority System. The system process C:\WINDOWS\SYSTEM32\LSASS.EXE terminated unexpectedly with status code 073741795. The system will shut down and restart in 60 seconds"

I've ran the a full scan with Microsoft Security Essentials and Malewarebytes Anti-Malware. I've also ran the Symantec removal tool for the MSBlast and Sasser virus and both scans came back clean, no signs of their respective viruses. I've ran the Microsoft Malicious Software tool and it came back clean as well. I'm at my wits end on what to do and I was hoping someone here might be able to provide a fix for me.

My HJT Log was run in safe mode with networking while logged in as an admin, as this is the only way I can log in. If I log in normally, the error message pops up before any icons or even the start button appear on the desktop.

Okay, I read the steps in the link provided and I was able to boot into normal mode, however, just like every time before, the message pops up as soon as windows loads so I am unable to run any programs. The first thing I have to do is click start-->run type cmd, press enter and then type shutdown -a. This stops the shutdown timer and allows me to stay logged on. However, I am unable to run my antivirus (Microsoft Security Essentials), MalewareByet's Anti Malware. MSE won't even turn on and MBAN locks up a few seconds in the scan... every time. I've tried downloading Avira and Avast, but when I click "Save" the browser locks up. I'm also unable to update my Java from version 6 update 24 to version 6 update 25. When I click on update, nothing happens at all... even after waiting for 10 minutes or longer. Also, I can't download and install anything, including HijackThis, in normal boot mode. I have it downloaded in safe mode though.

Below are the request logs in the order the scans were executed. Please note that I was unable to run my antivirus (Microsoft Security Essentials). When I tried to perform the scan, nothing happened. I let the scanning screen sit there for a good 10-15 minutes and there was absolutely no activity. I downloaded and installed Avira, linked in your 7 steps instructions, but it would not run, siting that it could not scan because there was a parallel Microsoft Update in progress. I was unable to find any evidence of this. I downloaded and installed Avast, linked in your 7 steps instructions, and it would not scan either, saying that the program was incorrectly installed and that I should reinstall it.

The remaining scans were executed in safe mode with networking enabled and I was logged in as Administrator.

**Note: In the event you already have Combofix, this is a new version that I need you to download. It is important that it is saved directly to your desktop**

Please, never rename Combofix unless instructed.

Close any open browsers.

Close/disable all anti virus and anti malware programs so they do not interfere with the running of ComboFix.

Very Important! Temporarily disable your anti-virus, script blocking and any anti-malware real-time protection before performing a scan. They can interfere with ComboFix or remove some of its embedded files which may cause "unpredictable results".

Click onthis linkto see a list of programs that should be disabled. The list is not all inclusive. If yours is not listed and you don't know how to disable it, please ask.

NOTE1. If Combofix asks you to install Recovery Console, please allow it.NOTE 2. If Combofix asks you to update the program, always do so.

Close any open browsers.

WARNING: Combofix will disconnect your machine from the Internet as soon as it starts

Please do not attempt to re-connect your machine back to the Internet until Combofix has completely finished.

If there is no internet connection after running Combofix, then restart your computer to restore back your connection.

Double click on combofix.exe & follow the prompts.

When finished, it will produce a report for you.

Please post the "C:\ComboFix.txt"

**Note 1: Do not mouseclick combofix's window while it's running. That may cause it to stall**Note 2 for AVG users: ComboFix will not run until AVG is uninstalled as a protective measure against the anti-virus. This is because AVG "falsely" detects ComboFix (or its embedded files) as a threat and may remove them resulting in the tool not working correctly which in turn can cause "unpredictable results". Since AVG cannot be effectively disabled before running ComboFix, the author recommends you to uninstall AVG first.
Use AppRemover to uninstall it: http://www.appremover.com/
We can reinstall it when we're done with CF.**Note 3: If you receive an error "Illegal operation attempted on a registery key that has been marked for deletion", restart computer to fix the issue.

Make sure, you re-enable your security programs, when you're done with Combofix.

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NOTE.
If, for some reason, Combofix refuses to run, try one of the following:

1. Run Combofix from Safe Mode.

2. Delete Combofix file, download fresh one, but rename combofix.exe to yourname.exeBEFORE saving it to your desktop.Do NOT run it yet.

Please download and run the below tool named Rkill(courtesy of BleepingComputer.com) which may help allow other programs to run.

There are 4 different versions. If one of them won't run then download and try to run the other one.

Vista and Win7 users need to right click Rkill and choose Run as Administrator

You only need to get one of these to run, not all of them. You may get warnings from your antivirus about this tool, ignore them or shutdown your antivirus.

Double-click SUPERAntiSpyware.exe and use the default settings for installation.

An icon will be created on your desktop. Double-click that icon to launch the program.

If asked to update the program definitions, click "Yes". If not, update the definitions before scanning by selecting "Check for Updates". (If you encounter any problems while downloading the updates, manually download and unzip them from here: http://www.superantispyware.com/definitions.html.)